I've been using it only for a very short amount of time (just downloaded this morning) and it's a pretty good program. Very simple to use and u can easily create some decent images with it. So just try it out, it's very simple to use and u will learn fast.
Here is a tutorial that tells u a little about the fuctions.http://www.planetside.co.uk/terragen/guide/

This was my 1st one and it took maybe like 15 mins so don't expect anything spectacular!

That looks good mammikoura I'l post some more once I have them... And John 123 I don't have Aim so I can't really help , but if you have msn I'm Hunter_Rocks_@hotmail.com and I would be happy to help you out , even though the guide posted is probably more help than me anyways Good luck guys!